The present invention relates to vapor vent valves for fuel tanks and particularly valves of the type that are float operated for controlling flow of fuel vapor from the tank to a storage device such as a canister filled with granulated carbonaceous material.
In providing such float operated vent valves for a motor vehicle fuel tank, it has been desired to provide multiple function valves in a common assembly for attachment to the tank through a single access opening in order to minimize the vapor permeation at the attachment. Such multiple function valves have included a plurality of float operated valves intended to close different sized vent ports at different levels of liquid fuel in the tank during refueling and in response to fuel sloshing in the tank during vehicle operation.
Typically, such multifunctional float operated valves require a substantial range of float, size, movement and buoyancy such that the float housing extends into the fuel tank to a significant degree. Thus, the housing is vulnerable to side loading as might be encountered in vehicle crashes and/or rollover conditions and damage to the housing which would then permit escape of vapor and liquid fuel from the tank into the atmosphere. Accordingly, it has been required to provide a redundancy or backup device for closing off the fuel vent ports in the event of valve damage vehicle collision or rollover.
Heretofore, such redundancy or backup for the float operated vent valves has been in the form of an additional float captured in the main valve body structure in a manner which is not susceptible to side loading in a collision which would result in loss of the float position. However, such backup valves require a high degree of flexibility and resiliency to the valve element for closing the vent port and to effect a complete seal in view of the relatively low mass of the backup float element and the minimal inertial or gravitational force available to close the valve in the event of rollover.
It is known to provide a relatively thin flexible elastomeric disk in the top of a relatively small float for providing backup closing of the vapor vent in the event of vehicle rollover for a multifunctional tank vapor vent valve. However, the attachment and retention of such a thin disk onto the float and requirement that the central portion of the disk remain exposed and resilient for closing the vent port has created problems in attachment of the disk-like member to the float. Accordingly, it has been desired to provide the simple and effective yet low cost way of providing a resilient valve member on a relatively small float for backup or redundant sealing of a vapor vent valve vent port in the event of vehicle rollover. In the manufacture of vehicle fuel tank vent valves of the float operated type, this type valve is often referred to as a “gutless” float valve.